This is a proposal to study the time course of changes in rabbit ear vascular resistance and structure after partial abdominal aortic constriction (PAAC). The specific aims include: (1) determination of the in vitro resistancae-flow-pressure-characteristics of the ear vascular bed from normotensive and hypertensive rabbits, (2) quantitation of the morphological parameters which are known to effect the vascular resistance directly i.e. the number, length and radius of the different sized vessels, (3) description in quantitative stereological terms of the components in the arterial wall which are responsible for the active and passive characteristics of the various sized arteries, (4) measurement of the size, orientation and number of medial smooth muscle cells using established methods of stereology, (5) quantitation of muscle cell and endothelial ultrastructure with regard to proportional composition and organization of the contractile apparatus, organelles and membranes. These studies will be pursued using a variety of approaches and techniques: (1) post-surgical constriction of the aorta to initiate time course studies, (2) vertical tube determination of flow-pressure curves for the ear vasculature with supporting constant flow and pressure measurements, (3) resistance measurement in response to sympathetic agonists and nerve stimulation, (4) pressure fixation under functionally defined conditions, (5) microangiographic and scanning electron microscopic determination of vascular geometry, (6) plastic embedding of tissues for light and transmission electron microscopy, (7) morphometry and stereology with the image analysis graphics computer system. In general, these studies should further our knowledge of correlation between basic functional and structural changes in developing hypertension. Specifically, the proposed study will investigate one intact vascular bed in detail to determine how changes in pressure and vascular resistance are related to morphometry of the vascular network and stereology of the vascular wall.